1. Field of the Invention
The present invention relates to an image processing apparatus for erasing a persistence of vision, so-called a residual image, in an output image signal of a TV camera.
2. Description of the Related Art
Recently, along with an improvement in technology of a television (TV) camera and a TV monitor, imaging is performed in various fields. In the field of X-ray diagnosing apparatus, an X-ray TV system has been developed in which, in stead of obtaining an X-ray radiograph of an object to be examined using an X-ray film, the X-ray image is converted into an optical image by an image intensifier, a fluoroscopic optical image is then picked up by a TV camera, and the fluoroscopic image is displayed on a TV monitor. If a stereoscopic X-ray tube having right and left focal points is used as an X-ray tube to radiate X-rays alternately from its right and left focal points, and right and left fluoroscopic images are picked up and observed by right and left eyes respectively, a stereoscopic X-ray TV system which can obtain a stereoscopic fluoroscopic image of the object to be examined can be realized, which is much more useful in diagnosis than a conventional two-dimensional X-ray imaging system.
In such a stereoscopic X-ray TV system, the right and left fluoroscopic images formed by the X-rays radiated from the right and left focal points are detected by one image intensifier and one TV camera. The right and left images must be strictly separated and respectively observed by right and left eyes. However, in a general TV camera, an image signal preceding the current image signal by one field or frame remains in the image signal of the current field or frame because of the residual image characteristic of the image pickup surface. Therefore, the right and left fluoroscopic images cannot be separately observed strictly by the right and left eyes. The right and left fluoroscopic images are mixed and displayed on a display screen, thereby the image cannot be observed stereoscopically. About 10% residual image normally remains in the image pickup surface of the TV camera.
The above description is given with reference to the stereoscopic X-ray TV system. However, an influence of the residual image is similarly found in a general imaging system using a TV camera.